Step-down DC/DC Converter with Voltage Detector

R1221N Series

‘99.12.8

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Rev. 1.11

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n OUTLINE

The R1221N Series are PWM step-down DC/DC Converter controllers embedded with a voltage detector, with

low supply current by CMOS process.

Each step-down DC/DC converter in these ICs consists of an oscillator, a PWM control circuit, a reference

voltage unit, an error amplifier, a soft-start circuit, a protection circuit, a PWM/VFM alternative circuit, a chip

enable circuit, and resistors for voltage detection. A low ripple, high efficiency step-down DC/DC converter can be

composed of this IC with only four external components, or a power-transistor, an inductor, a diode and a

capacitor.

The output voltage of DC/DC converter can be supervised by the built-in voltage detector.

With a PWM/VFM alternative circuit, when the load current is small, the operation turns into the VFM oscillator

from PWM oscillator automatically, therefore the efficiency at small load current is improved.

And the PWM/VFM alternative circuit is an option, in terms of C version and D version, the circuit is not included.

If the term of maximum duty cycle keeps on a certain time, the embedded protection circuit works. There are two

types of protection function. One is latch-type protection circuit, and it works to latch an external Power MOS with

keeping it disable. To release the condition of protection, after disable this IC with a chip enable circuit, enable it

again, or restart this IC with power-on. The other is Reset-type protection circuit, and it works to restart the

operation with soft-start and repeat this operation until maximum duty cycle condition is released. Either of these

protection circuits can be designated by users’ request.

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n FEATURES

l Wide Range of Input Voltage · · · · · · · · · · · · · 2.3V to 13.2V

l Built-in Soft-start Function and two choices of Protection Function(Latch-type or Reset-type)

l Two choices of Oscillator Frequency · · · · · · · · · · 300kHz, 500kHz

l High Efficiency · · · · · · · · · · · · · · · · · · · · · · TYP. 90%

l Standby Current · · · · · · · · · · · · · · · · · · · · · TYP. 0µA

l Setting Output Voltage · · · · · · · · · · · · · · · · · Stepwise setting with a step of 0.1V in the range of

1.5V to 5.0V

l High Accuracy Output Voltage · · · · · · · · · · · · · · ±2.0%

l Setting Detector Threshold Voltage · · · · · · · · · · · Stepwise setting with a step of 0.1V in the range of

1.2V to 4.5V

l High Accuracy Detector Threshold Voltage· · · · · · · ±2.0%

l Low Temperature-Drift Coefficient of Output Voltage · TYP. ±100ppm/°C

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n APPLICATIONS

l Power source for hand-held communication equipment, cameras, video instruments such as VCRs,

camcorders.

l Power source for battery-powered equipment.

l Power source for household electrical appliances.